The invention relates to an apparatus as defined in the preamble of claim 1 for discharging different kinds of material from a silo or a corresponding container.
Silos are used for the storage of various kinds of bulk material, such as different wood fractions used as raw material for various processes or as fuel in boilers for energy production.
In particular, such materials include unsorted wood waste materials used as fuel, such as bark, screening waste, waste from demolished buildings, knots and other less valuable wood material. Another type of fuel are the so-called forest processed chips, which contain large amounts of unsorted components, such as twigs, needles and pieces of wood.
It is not expedient to grade or homogenize bulk material to be used as fuel because such material will burn in a boiler even if consists of larger particles.
However, this kind of non-uniform mixed material is difficult to handle, and problems are especially encountered in discharging such material from a silo because the material tends to cake together and does not flow down readily by itself and because the longer particles in it cause feed disturbances.
Usually this type of cumbersome material is unloaded from a silo by using linearly operated rake or pole dischargers by which the material in the silo is discharged through a lateral discharge opening for further transport to the site of use.
Dischargers of this type are particularly heavy in structure and need a high operating power because they have to move material simultaneously over the whole area of the silo bottom and "ram" it in one or two directions. Moreover, these systems are disadvantageous in respect of space utilization e.g. because the hydraulic drive requires a large space.
An additional disadvantage with silos of rectangular design is the heavy structure of their flat side walls.
Discharging methods in which the material is discharged through the center of the silo have the disadvantage that the material is moved through convergent holes and complex channels in which nonhomogeneous and setting material tends to cause disturbances as referred to above, which is why such methods are in many cases unusable.
An example of this type of dischargers which discharge the material through the center of the silo is the one presented in DE patent 1133310. It has the disadvantage that the material is discharged into a space convergent towards the center of the silo. Another drawback is that the discharge ring tends to move upwards when close to the silo walls as the ring is rotated by toothing placed on the inside of the ring. These facts are a source of problems in practical work. The same drawbacks are also observed in the apparatus proposed by Finnish patent application FI 832214.
The object of the present invention is to create an expanding free space within the silo to ensure the discharge of any compressed and set material in the silo.
This object is solved by the features defined in the characterising portion of claim 1.
In a preferred embodiment of the invention, the discharge ring is driven by a toothing placed on the circumference of the discharge ring and the ring is retained by its rim to prevent it from rising and provided with a contact to prevent rotation in the same place.
With the apparatus of the invention, the content material is unloaded from under the shell of a round-bottom silo through a ringlike discharge opening placed on or close to the circumference of the silo bottom. The content material moves radially on the silo bottom towards an expanding free space, so that the material, which has been under a pressure in the silo, can now be loosened, thereby ensuring the discharge of any compressed and set material.
The silo discharger of the invention has a low operating power because the material is only handled at a variable discharge point and the material movement inside the silo is as short as possible because of its radial nature.
Using the apparatus of the invention, the material can easily be uniformly discharged from the whole area of the silo bottom. This property permits the material stored in the silo to be handled in a first-in first-out manner, ensuring a uniform retention time. This circumstance is of a decisive importance in cases where the material in the silo is subjected e.g. to thermal or chemical treatment as a function of time (steaming, bleaching etc.).
The content material discharged from a silo using the apparatus of the invention is typically gathered in a collection space provided under the silo bottom, from where the material is conveyed further by known methods.
The collection space under the silo can also advantageously be used for further treatment of the material, e.g. dilution, mixing of chemicals etc. The structure and design of the collection space are adapted to the intended use.
Different versions of the apparatus of the invention can be provided with suitable accessories e.g. for the mixing of materials in the collection space.
Instead of a collection space, further conveyance of the material can also be implemented using a conveyor circulating around the silo bottom, a blast conveyor or the like.
In the following, the invention will be described by the aid of an example, reference being made to the attached drawings, in which
Figures 1, 2 and 3 show a silo 1 used for the storage of content material 2, which is supplied into the silo through an opening 3. The silo has a bottom 10 which is provided with a discharge opening 13, preferably of a ringlike shape. To empty the silo, i.e. to discharge the content material from the silo, one or more discharge rings 9 are rotated by a drive system comprising a drive 4, a power transmission gear 7 and a drive wheel 8 connected to its secondary shaft. The drive wheel 8 is preferably provided with shaft journals and teeth. By rotating the drive wheel 8, the discharge ring 9 is caused to rotate about its own center B and B' and simultaneously to turn about another axis C and C', preferably the vertical axis of the silo.
Placed on or near the radially outermost orbit of the discharge ring(s) 9 is/are one or more support elements which is/are in contact 20 with the discharge ring/discharge rings 9. This prevents the discharge ring/discharge rings 9 from rotating in the same place. The support element 11 is a circular body or the support elements 11 are placed on the circumference of a circle and it is provided with/they are elements adapted to the toothing 19 or equivalent formed on the periphery of the discharge ring/rings 9, such as counter toothings, pins, notches, holes or the like.
An advantageous solution to achieve a contact 20 is to use a counter toothing 11 adapted to the toothing 19 on the circumference of the discharge ring 9. It is also possible to use e.g. a frictional contact between the discharge ring and the ring on the circumference of the silo. The support element/elements 11 is/are placed on the circumference of the silo and are preferably attached to its interior surface or formed as parts of the interior surface. Formed on or attached to the support element is an element which is placed against the top surface of the discharge ring to prevent the latter from rising.
The discharge ring/rings 9 is/are typically provided with a bevelling 18 on the interior edge to permit the material to be more easily passed under it during the backward motion D' The discharge rings 9 are placed on top of the silo bottom 10, preferably in its immediate vicinity or in contact with the bottom (10).
As the discharge ring/rings 9 turns/turn C and C' around the bottom, it/they push the material with its/their outer edge radially D from under the shell 12 of the silo 1 into the discharge opening 13 and further into the collection space 14 and onto a conveyor 15.
The material is uniformly discharged from the entire area of the silo bottom 10 according to the first-in first-out principle. Since the material discharge occurs radially D from under 12 the shell of the silo 1 into a free space 13 at the outer edge, the discharging does not require much work and therefore the power requirement is small as compared with previously known discharging methods used for corresponding materials.
Fig. 2 presents another embodiment in accordance with the invention in which the collection space consists of a mixing container 17. Mounted in the mixing container are mixing elements 16, to which the driving power is transmitted from the drive 4 via the power transmission gear 7. For example, when high-consistency pulp is to be diluted to a consistency suitable for pumping, this embodiment is very useful as the material is discharged uniformly from the entire area of the the silo bottom and the discharging into the mixing container is performed in the manner described above. It is clear from the above examples, e.g. from the solutions presented in Fig. 1, 2 and 3, that the apparatus of the invention has an advantageous structure which enables it to be used in demanding conditions and applications as explained above.
It is obvious to a person skilled in the art that the invention is not restricted to the embodiments described above, but that it may be varied within the scope of the following claims.